Both Democrats and Republicans are awaiting answers on whether Comey had evidence that Trump's campaign had colluded with Russian officials during last year's presidential election, and are expected to ask for details regarding previous interactions between Comey and Trump.

The men were testifying on the Foreign Intelligence Surveillance Act (FISA), but the hearing on several occasions veered into Comey's firing, as well as the ongoing investigation into Russian meddling in last year's presidential election.

Where can I watch it?

All the major networks (ABC, NBC, and CBS) will interrupt their usual programming to broadcast the hearing, and all the cable news channels (C-SPAN, CNBC, MSNBC, CNN, and Fox News) will carry it as well.

Who's participating?

There are 15 members of the bipartisan Senate Intelligence Committee, and they run the gamut in terms of their spot on the political spectrum.

Republicans such as chairman Richard Burr of North Carolina and moderate Susan Collins of Maine have already been pegged as senators to watch, as well as frequent Trump critic Marco Rubio of Florida and Trump supporter John Cornyn of Texas.

On the Democratic side, Senator Ron Wyden of Oregon is a prominent Comey critic but opposed his firing, and Kamala Harris of California has been a particularly vocal critic of the Trump administration.

What will Comey say?

It's unclear what questions Comey will answer. He has already spoken with newly appointed special counsel Robert Mueller — who has taken over the FBI's Russia investigation — regarding his testimony, and Comey will likely not divulge any new information on the probe, his associates told Politico.

Instead, Comey's testimony will mostly revolve around his own conversations with Trump. "[Comey] wants to correct the record, from is point of view, on certain things the president and his aides have said," one Comey associate told Politico.

What will Trump be doing?

Trump is set to give a speech to religious conservatives at the Faith and Freedom Coalition's "Road to Majority" conference during Comey's testimony, but The Washington Post's Robert Costa reported that Trump "may" also live tweet the hearing before or after his speech "if he feels the need to respond" to Comey's remarks.

When Trump was asked on Tuesday about Comey's upcoming hearing, the president said, "I wish him luck."